Preparation of azo colorants in microreactors

ABSTRACT

Azo colorants are prepared by conducting the diazotization of aromatic or hetaromatic amines or the azo coupling reaction or the diazotization and the azo coupling reaction in a microreactor.

[0001] The present invention is described in the German priority applications No. 10005550.8, filed Feb. 9, 2000, and No. 10040100.7, filed Aug. 16, 2000, which are hereby incorporated by reference as is fully disclosed herein.

[0002] The present invention relates to the field of azo colorants. Azo colorants are customarily produced in industry in batch operations in reaction vessels by mixing the starting materials together in aqueous phase (Fisher, Organische Chemie, Verlag Chemie, Weinheim/Bergstraβe, 1965, p. 890 ff., 1431, 1796 ff.).

[0003] Another way is the continuous mixing of equivalent amounts of the starting materials in the form of aqueous acidic or aqueous alkaline solutions in, for example, mixing nozzles and continuous flow reactors with or without a postreaction phase in a reaction vessel (azo coupling: DE 1 544 453, EP 244 686; diazotization: EP-A-0 006 190).

[0004] The principal process operations involved are the diazotization of aromatic or hetaromatic amines and the azo coupling reaction. Certain azo pigments may subsequently require a metal exchange reaction (laking) and/or an aftertreatment in water/solvents to obtain the desired crystal properties. In the case of some azo dyes, a reaction is subsequently carried out to form metal complexes.

[0005] In all these processes, it is essential that the process parameters, such as temperature, time and (in the case of azo pigments) also in particular the degree of mixing, be controlled, if the products are to be pure and of high and consistent quality. One problem with these processes is the scaleup of new products from the laboratory scale to the large industrial scale.

[0006] It is an object of the present invention to provide a process for preparing azo colorants that provides optimal control of the process parameters, ensures improved mixing of the reactants and simplifies scaleup.

[0007] DD 246 257 A1 discloses the possibility of using miniaturized apparatuses for chemical reactions where the chemical entities to be treated are only available in small quantities or are very costly, so that large dead spaces in the equipment become unaffordable. DE 3 926 466 C2 describes strong exothermic chemical reactions of two chemical entities in a microreactor.

[0008] Microreactors for chemical reactions are constructed from stacks of grooved plates and are described in DE 39 26 466 C2 and U.S. Pat. No. 5,534,328. It is pointed out in U.S. Pat. No. 5,811,062 that microchannel reactors are preferably used for reactions that do not require or produce materials or solids that would clog the microchannels.

[0009] It has now been found that, surprisingly, microreactors are useful for carrying out diazotization and azo coupling and also metal exchange reactions or metal complexing reactions to prepare azo colorants, such as azo pigments and azo dyes.

[0010] As used herein, microreactor comprehends micro- and minireactors, which differ only by reason of the dimensions and construction of the reaction channel structures.

[0011] It is possible to use, for example, microreactors as known from the cited references or from publications of the Institut für Mikrotechnik Mainz GmbH, Germany, or else commercially available microreactors, for example Selecto™ (based on Cytos™) from Cellular Process Chemistry GmbH, Frankfurt/Main.

[0012] The invention accordingly provides a process for preparing azo colorants by conducting the diazotization of aromatic or hetaromatic amines or the azo coupling reaction or the metal exchange reactions or the metal complexing reactions or the diazotization and the azo coupling reaction and the metal exchange or metal complexing reactions in a microreactor.

[0013] Advantageously, the preferably aqueous solutions or suspensions of the starting materials are fed to the microreactor continuously and preferably in equivalent amounts. The classic process assistants such as resins, surfactants and other additives may likewise be used in the process of the invention.

[0014] The starting materials for the diazotization reaction are aromatic or hetaromatic amines or their ammonium salts, for example aniline, 2-nitroaniline, methyl anthranilate, 2,5-dichloroaniline, 2-methyl-4-chloroaniline, 2-chloroaniline, 2-trifluoromethyl-4-chloroaniline, 2,4,5-trichloroaniline; 3-amino-4-methylbenzamide, 2-methyl-5-chloroaniline, 4-amino-3-chloro-N′-methylbenzamide, o-toluidine, o-dianisidine, 2,2′,5,5′-tetrachlorobenzidine, 2-amino-5-methylbenzenesulfonic acid, 2-amino-4-chloro-5-methylbenzenesulfonic acid.

[0015] Of particular interest for azo pigments are the following amine components: 4-methyl-2-nitrophenylamine, 4-chloro-2-nitrophenylamine, 3,3′-dichlorobiphenyl-4,4′-diamine, 3,3′-dimethylbiphenyl-4,4′-diamine, 4-methoxy-2-nitrophenylamine, 2-methoxy4-nitrophenylamine, 4-amino-2,5-dimethoxy-N-phenylbenzenesulfonamide, dimethyl 5-aminoisophthalate, anthranilic acid, 2-trifluoromethylphenylamine, dimethyl 2-aminoterephthalate, 1,2-bis(2-aminophenoxy)ethane, diisopropyl 2-aminoterephthalate, 2-amino-4-chloro-5-methylbenzenesulfonic acid, 2-methoxyphenylamine, 4-(4-aminobenzoylamino)benzamide, 2,4-dinitrophenylamine, 3-amino-4-methylbenzamide, 3-amino-4-chlorobenzamide, 3-amino-4-chlorobenzoic acid, 4-nitrophenylamine, 2,5-dichlorophenylamine, 4-methyl-2-nitrophenylamine, 2-chloro-4-nitrophenylamine, 2-methyl-5-nitrophenylamine, 2-methyl-4-nitrophenylamine, 2-methyl-5-nitrophenylamine, 2-amino-4-chloro-5-methylbenzenesulfonic acid, 2-aminonaphthalene-1-sulfonic acid, 2-amino-5-chloro-4-methylbenzenesulfonic acid, 2-amino-5-chloro-4-methylbenzenesulfonic acid, 2-amino-5-methylbenzenesulfonic acid, 2,4,5-trichlorophenylamine, 3-amino-4-methoxy-N-phenylbenzamide, 4-aminobenzamide, methyl 2-aminobenzoate, 4-amino-5-methoxy-2,N-dimethylbenzenesulfonamide, monomethyl 2-amino-N-(2,5-dichlorophenyl)terephthalate, butyl 2-aminobenzoate, 2-chloro-5-trifluoromethylphenylamine, 4-(3-amino-4-methylbenzoylamino)benzenesulfonic acid, 4-amino-2,5-dichloro-N-methylbenzenesulfonamide, 4-amino-2,5-dichloro-N,N-dimethylbenzenesulfonamide, 6-amino-1H-quinazolin-2,4-dione, 4-(3-amino-4-methoxybenzoylamino)benzamide, 4-amino-2,5-dimethoxy-N-methylbenzenesulfonamide, 5-aminobenzimidazolone, 6-amino-7-methoxy-1,4-dihydroquinoxalin-2,3-dione, 2-chloroethyl 3-amino-4-methylbenzoate, isopropyl 3-amino-4-chlorobenzoate, 3-amino-4-chlorobenzotrifluoride, n-propyl 3-amino-4-methylbenzoate, 2-aminonaphthalene-3,6,8-trisulfonic acid, 2-aminonaphthalene-4,6,8-trisulfonic acid, 2-aminonaphthalene-4,8-disulfonic acid, 2-aminonaphthalene-6,8-disulfonic acid, 2-amino-8-hydroxynaphthalene-6-sulfonic acid, 1-amino-8-hydroxynaphthalene-3,6-disulfonic acid, 1-amino-2-hydroxybenzene-5-sulfonic acid, 1-amino-4-acetylaminobenzene-2-sulfonic acid, 2-aminoanisole, 2-aminomethoxybenzene-ω-methanesulfonic acid, 2-aminophenol-4-sulfonic acid, o-anisidine-5-sulfonic acid, 2-(3-amino-1,4-dimethoxybenzenesulfonyl)ethyl sulfate and 2-(1-methyl-3-amino-4-methoxybenzenesulfonyl)ethyl sulfate.

[0016] The following amine components are of particular interest for azo dyes: 2-(4-aminobenzenesulfonyl)ethyl sulfate, 2-(4-amino-5-methoxy-2-methylbenzenesulfonyl)ethyl sulfate, 2-(4-amino-2,5-dimethoxybenzenesulfonyl)ethyl sulfate, 2-[4-(5-hydroxy-3-methylpyrazol-1-yl)benzenesulfonyl]ethyl sulfate, 2-(3-amino-4-methoxybenzenesulfonyl)ethyl sulfate, 2-(3-aminobenzenesulfonyl)ethyl sulfate. The amine to be diazotized, or its ammonium salt, preferably its hydrochloride or sulfate, is preferably dissolved or suspended in water and/or an organic solvent and the resulting solution or suspension is continuously introduced into the microreactor (reactant stream A).

[0017] Concurrently, a solution or suspension, preferably an aqueous solution or suspension, of a diazotizing agent, preferably NaNO₂ or nitrosylsulfuric acid, is continuously introduced into the microreactor (reactant stream B). In the reactor, reactant streams A and B are continuously mixed with each other and reacted.

[0018] The starting materials for azo coupling reactions are diazonium salts, for example as above-mentioned or -prepared, and coupling components in solution or suspension.

[0019] The following coupling components are of particular interest for azo pigments: acetoacetarylides

[0020] and R_(k)=CH₃, OCH₃, OC₂H₅, NO₂, Cl, NHCOCH₃ and n=0 to 3; and also R₂=H, CH₃ and C₂H₅,

[0021] bisacetoacetylated diaminobenzenes and -biphenyls, N,N′-bis(3-hydroxy-2-naphthoyl)phenylenediamines (each optionally substituted), and also pyrazolones

[0022] where

[0023] R=CH₃, COOCH₃, COOC₂H₅,

[0024] R′=CH₃, SO₃H, Cl;

[0025] p=0 to 3.

[0026] The following coupling components are of particular interest for azo dyes: 4-[5-hydroxy-3-methylpyrazol-1-yl]benzenesulfonic acid, 2-aminonaphthalene-1,5-disulfonic acid, 5-methoxy-2-methyl-4-[3-oxobutyrylamino]benzenesulfonic acid, 2-methoxy-5-methyl-4-[3-oxobutyrylamino]benzenesulfonic acid, 4-acetylamino-2-aminobenzenesulfonic acid, 4-[4-chloro-6-(3-sulfophenylamino)-[1,3,5]-triazin-2-yl-amino]-5-hydroxynaphthalene-2,7-disulfonic acid, 4-acetylamino-5-hydroxynaphthalene-2,7-disulfonic acid, 4-amino-5-hydroxynaphthalene-2,7-disulfonic acid, 5-hydroxy-1-[4-sulfophenyl]-1H-pyrazole-3-carboxylic acid, 2-aminonaphthalene-6,8-disulfonic acid, 2-amino-8-hydroxynaphthalene-6-sulfonic acid, 1-amino-8-hydroxynaphthalene-3,6-disulfonic acid, 2-aminoanisole, 2-aminomethoxybenzene-ω-methanesulfonic acid and 1,3,5-trishydroxybenzene.

[0027] The azo coupling is preferably carried out in aqueous solution, but it is also possible to use organic solvents, if appropriate mixed with water, for example aromatic hydrocarbons, hydrochlorocarbons, glycol ethers, nitriles, esters, dimethylformamide, tetramethylurea and N-methylpyrrolidone.

[0028] To carry out the azo coupling reaction according to the invention, a solution or suspension of the diazonium salt (reactant stream C) and a solution or suspension of the coupling component (reactant stream D) are continuously introduced into the microreactor and continuously mixed with each other therein and reacted.

[0029] The starting materials for laking are azo colorants that contain acid groups, in the form of the free acids or their, for example, alkali metal salts or salts of alkaline earth metals, ammonium salts or aluminum or manganese salts.

[0030] To lake azo pigments, a metal salt solution, for example an aqueous calcium, strontium bromine or manganese salt solution (reactant stream E), is mixed with the solution or suspension of an azo colorant that contains acid groups (reactant stream F), and brought to a temperature between 30 and 100° C., in the microreactor. The laking reaction takes place in the reactor itself or is initiated there. The reaction may be completed in a downstream continuous tubular reactor (delay vessel).

[0031] For the purposes of the present invention, not only the diazotization, the azo coupling reaction but also the laking reaction or the metal complexing reaction may each be carried out in (successive) microreactors, or the diazotization is carried out in a conventional manner and only the azo coupling reaction is carried out in the microreactor, or the diazotization is carried in the microreactor and the azo coupling is carried out in a conventional manner. Similarly, the laking may in each case be carried out conventionally or else in a microreactor. It is also possible to use microreactors having two or more reaction zones for the individual reaction steps.

[0032] A microreactor is constructed from a plurality of laminae which are stacked and bonded together and whose surfaces bear micromechanically created structures which interact to form reaction spaces for chemical reactions. The system contains at least one continuous channel connected to the inlet and the outlet.

[0033] The flow rates of the material streams are limited by the apparatus, for example by the pressures which result depending on the geometry of the microreactor. It is desirable for the reaction to take place completely in the microreactor, but it is also possible to adjoin a delay zone to create a delay time that may be required.

[0034] The flow rates are advantageously between 0.05 and 5 l/min, preferably between 0.05 and 500 ml/min, particularly preferably between 0.05 and 250 ml/min, especially between 0.1 and 100 ml/min.

[0035] A microreactor useful for preparing azo colorants is described in FIG. 1 by way of example.

[0036] The present microreaction system is constructed from six microstructured metal laminae, stacked and bonded together, plus a lid plate (LP) and a base plate (BP) to form a processing module that is firmly held or bonded together to compress sealing sheets between the plates.

[0037] The present microreaction system includes two heat exchangers for cooling and/or heating medium, a mixing zone for mixing the reactants and a short delay zone.

[0038] The heat exchanger (W1) preheats the reactant streams flowing separately into plate (E). The reactant streams are then mixed within plates (M), which form a conjoint space. The delay zone (R) brings the reaction mixture to the desired reaction temperature with the aid of the heat exchanger (W2), so that the desired chemical reaction can take place.

[0039] The microreaction system is operated continuously, and the fluid quantities which are mixed with each other in each case are in the microliter (μl) to milliliter (ml) region.

[0040] The dimensions of the microstructured regions within the reactor are decisive for preparing azo colorants in this microreaction system. These dimensions have to be sufficiently large that, in particular, solid particles can pass through without problem and so do not clog up the channels. The smallest clear width of the microstructures should be about ten times larger than the diameter of the largest pigment particles. Furthermore, it has to be ensured, by appropriate geometric styling, that there are no dead water zones, for example dead ends or sharp corners, where for example pigment particles could sediment. Preference is therefore given to continuous paths having round corners. The structures have to be sufficiently small to exploit the intrinsic advantages of microreaction technology, namely excellent heat control, laminar flow, diffuse mixing and low internal volume.

[0041] The clear width of the solution- or suspension-ducting channels is advantageously 5 to 10 000 μm, preferably 5 to 2 000 μm, particularly preferably 10 to 800 μm, especially 20 to 700 μm.

[0042] The clear width of the heat exchanger channels depends primarily on the clear width of the liquid- or suspension-ducting channels and is advantageously not more than 10 000 μm, preferably not more than 2 000 μm, especially not more than 800 μm. The lower limit of the clear width of the heat exchanger channels is uncritical and is at most constrained by the pressure increase of the heat exchanger fluid to be pumped and by the necessity for optimum heat supply or removal.

[0043] The dimensions of the microreaction system used are: Heat exchanger structures: channel width ˜600 μm channel height ˜250 μm Mixer and delay time: channel width ˜600 μm channel height ˜500 μm

[0044] The six superposed and closely conjoined metal laminae are preferably supplied with all heat exchanger fluids and reactants from above. The product and the heat exchanger fluids are preferably likewise removed upwardly. The possible supply of third and fourth liquids involved in the reaction (eg. buffer solutions) is realized via a T-junction located directly upstream of the reactor (FIG. 2), ie. one reactant can be premixed with the buffer solution. The requisite concentrations and flows are preferably controlled via precision piston pumps and a computer-controlled control system. The reaction temperature is monitored via integrated sensors and monitored and controlled with the aid of the control system and of a thermostat/cryostat.

[0045] The preparation of mixtures of feedstocks to form material streams may also be carried out in advance in micromixers or in upstream mixing zones. It is also possible for feedstocks to be metered into downstream mixing zones or into downstream micromixers or -reactors.

[0046] The system used here is made of stainless steel; other materials, for example glass, ceramic, silicon, plastics or other metals, may also be used.

[0047] Diazotizations are carried out at temperatures of −10 to +80° C., preferably −5 to +30° C., and azo couplings at 0 to 90° C., preferably at 10 to 60° C.

[0048] For both the diazotization and the azo coupling, the reactant streams may be admixed with buffer solutions, preferably of organic acids and salts thereof, for example acetic acid/acetate buffer, citric acid/citrate buffer, or of inorganic acids and salts thereof, for example phosphoric acid/phosphate or carbonic acid/carbonate.

[0049] The process of the invention provides high reaction rates with significantly higher reaction temperatures than, for example, in the batch process. More particularly, temperature-sensitive reactants, for example diazonium salts and alkaline solutions of 2-hydroxy-3-naphtharylides, can be reacted with advantage. The high heat transfer rate during the short residence time in the micro- or minireactor makes it possible to realize a short thermal stress of the reactant within a narrowly definable time window.

[0050] The process of the invention provides azo colorants, such as azo pigments and azo dyes.

[0051] Azo pigments may be monoazo or disazo (laked and unlaked) pigments. It is also possible to prepare mixtures of azo pigments. Contemplated azo pigments are in particular C.I. Pigment Yellow 1, 3, 12, 13, 14, 16, 17, 65, 73, 74, 75, 81, 83, 97, 111, 120, 126, 127, 151, 154, 155, 174, 175, 176, 180, 181, 183, 191, 194, 198; Pigment Orange 5, 34, 36, 38, 62, 72, 74; Pigment Red 2, 3, 4, 8, 12, 14, 22, 48:1-4, 49:1, 52:1-2, 53:1-3, 57:1, 60:1, 112, 137, 144, 146, 147, 170, 171, 175, 176, 184, 185, 187, 188, 208, 214, 242, 247, 253, 256, 266; Pigment Violet 32; Pigment Brown 25.

[0052] With regard to dyes, disperse dyes are contemplated as well as water-soluble anionic and cationic dyes. Contemplated dyes are in particular mono-, dis- or polyazo dyes and also formazan or anthraquinone dyes. Water-soluble dyes are in particular the alkali metal salts or ammonium salts of reactive dyes and also of acidic wool dyes or direct cofton dyes of the azo series. Contemplated azo dyes are preferably metal-free and metallizable monoazo, disazo and trisazo dyes containing one or more sulfonic acid or carboxylic acid groups, heavy metal-containing, namely copper-, chromium or cobalt-containing monoazo, disazo and trisazo dyes. The intermediates for the metal-containing dyes may be prepared by the customary method in a conventional batch process. The subsequent metal complexing reaction, for example with copper ions, is then preferably carried out at temperatures between 30 and 100° C. in a microreactor.

[0053] Contemplated reactive azo dyes are in particular C.I. Reactive Yellow 15, 17, 37, 57, 160; Reactive Orange 107; Reactive Red 2, 23, 35, 180; Reactive Violet 5; Reactive Blue 19, 28, 203, 220; and Reactive Black 5, 8, 31.

[0054] This process also provides in particular C.I. Acid Yellow 17, 23; Direct Yellow 17, 86, 98, 132, 157; and Direct Black 62, 168 and 171.

[0055] It is surprising and was unforeseeable that the production of azo colorants is possible in this technically elegant way, since it was hitherto assumed that the production of solids in the microreactor would cause the system to clog up.

[0056] The azo pigments prepared according to the invention are useful for pigmenting macromolecular organic materials of natural or synthetic origin, for example plastics, resins, coatings, paints or electrophotographic toners and developers and also inks, including printing inks.

[0057] The azo dyes prepared according to the invention are useful for dyeing or printing hydroxyl-containing or nitrogenous natural organic and also synthetic substrates. Such substrates include for example synthetic or natural fiber materials and also leather materials comprising predominantly natural or regenerated cellulose or natural or synthetic polyamides. They are particularly useful for dyeing and printing textile material based on acetate, polyester, polyamide, polyacrylonitrile, PVC and polyurethane fibers and also wool or in particular cofton. To this end, the dyes can be applied to the textile materials by the usual exhaust, padding or printing processes.

[0058] The azo colorants prepared according to the invention are useful as colorants in electrophotographic toners and developers, for example one- or two-component powder toners (also known as one- or two-component developers), magnet toners, liquid toners, latex toners, polymerization toners and also specialty toners.

[0059] Typical toner binders are addition polymerization, polyaddition and polycondensation resins, such as styrene, styrene-acrylate, styrene-butadiene, acrylate, polyester, phenol-epoxide resins, polysulfones, polyurethanes, individually or in combination, and also polyethylene and polypropylene, which may each include further ingredients, such as charge control agents, waxes or flow assistants, or are subsequently modified with these additives.

[0060] The azo colorants prepared according to the invention are further useful as colorants in powders and powder coatings, especially in triboelectrically or electrokinetically sprayable powder coatings used for surface coating of objects composed for example of metal, wood, plastic, glass, ceramic, concrete, textile material, paper or rubber.

[0061] Powder coating resins used are typically epoxy resins, carboxyl- and hydroxyl-containing polyester resins, polyurethane and acrylic resins together with customary hardeners. Combinations of resins are also used. For instance, epoxy resins are frequently used in combination with carboxyl- and hydroxyl-containing polyester resins. Typical hardener components (depending on the resin system) include for example acid anhydride, imidazoles and also dicyandiamide and derivatives thereof, capped isocyanates, bisacylurethanes, phenolic and melamine resins, triglycidyl isocyanurates, oxazolines and dicarboxylic acids.

[0062] The azo colorants prepared according to the invention are also useful as colorants in inks, preferably inkjet inks, for example on an aqueous or nonaqueous basis, microemulsion inks and also in such inks as operate according to the hot-melt principle.

[0063] Inkjet inks generally include a total of 0.5 to 15% by weight, preferably 1.5 to 8% by weight, (reckoned dry) of one or more of the compounds according to the invention. Microemulsion inks are based on organic solvents and water with or without an additional hydrotropic substance (interface mediator). Microemulsion inks include 0.5 to 15% by weight, preferably 1.5 to 8% by weight, of one or more of the compounds according to the invention, 5 to 99% by weight of water and 0.5 to 94.5% by weight of organic solvent and/or hydrotropic compound.

[0064] Solvent based inkjet inks preferably include 0.5 to 15% by weight of one or more compounds according to the invention, 85 to 99.5% by weight of organic solvent and/or hydrotropic compounds.

[0065] Hot-melt inks are based mostly on waxes, fatty acids, fatty alcohols or sulfonamides that are solid at room temperature and liquefy on heating, the preferred melting range lying between about 60° C. and about 140° C. Hot-melt inkjet inks consist essentially for example of 20 to 90% by weight of wax and 1 to 10% by weight of one or more of the compounds according to the invention. They may further include 0 to 20% by weight of an additional polymer (as “dye solvent”), 0 to 5% by weight of dispersant, 0 to 20% by weight of viscosity modifier, 0 to 20% by weight of plasticizer, 0 to 10% by weight of tack additive, 0 to 10% by weight of transparency stabilizer (prevents crystallization of waxes, for example) and also 0 to 2% by weight of antioxidant. Typical additives and assistants are described for example in U.S. Pat. No. 5,560,760.

[0066] The azo colorants prepared according to the invention are also useful as colorants for color filters and also for additive as well as subtractive color generation.

[0067] Percentages are by weight in the examples, hereinbelow.

EXAMPLE 1 C.I. Pigment Red 2

[0068] a) Preparation of a Diazonium Salt Solution:

[0069] A 500 ml three-neck flask is charged with 14.6 g of solid 2,5-dichloroaniline in 25.1 ml of water, and 30.8 ml of 31% hydrochloric acid are added. The mixture is stirred at RT for 8 hours to provide a hydrochloride solution. On addition of a further 25.1 ml of water and 3.75 ml of 60% acetic acid the reaction mixture is cooled to −5° C. At this temperature, 11.5 ml of 40% sodium nitrite solution are added dropwise to the reaction mixture over about 15 min and stirred in at 0° C. for a further 60 min. The reaction mixture is clarified by adding six spatula tipfuls of Celite and rapidly filtering with suction. The yellowish diazonium salt solution is made up with water to a total volume of 300 ml (˜0.3 M).

[0070] b) Preparation of a Solution of the Coupling Component:

[0071] A second flask is charged with 23.9 g of Naphtol AS in 50.2 ml of water, and 26.7 ml of 25% aqueous sodium hydroxide solution are added. This mixture is then stirred at 60° C. for 120 min to dissolve it. It is rapidly filtered with suction and likewise made up with water to a total volume of 300 ml (˜0.3 M).

[0072] c) Azo Coupling in Microreactor

[0073] The conventionally prepared diazonium salt and Naphtol solutions are pumped via calibrated piston pumps into the respective reactant inlets of the microreactor at a flow rate of 6 ml/min in each case. The actual azo coupling takes place in the reactor space. To obtain a buffering effect, these reactant solutions are diluted with an acetic acid solution (4 ml of 60% acetic acid and 600 ml of water) shortly upstream of the reactor inlets. The acetic acid solution is likewise fed at a flow rate of 6 ml/min into the reactant feed lines of the microreactor via a T-junction by means of calibrated piston pumps. The heat exchanger circuit of the microreactor is connected to a thermostat which ensures a reaction temperature of 40° C. At the reactor outlet the product suspension pH is about 3. The product suspension emerging from the reactor is collected in a flask, filtered off with suction and washed neutral with water. The moist C.I. Pigment Red 2 is dried at 65° C.

EXAMPLE 2

[0074] a) Preparation of a Hydrochloride Solution of 2,5-Dichloroaniline

[0075] A 500 ml three-neck flask is charged with 14.6 g of solid 2,5-dichloroaniline in 25.1 ml of water, 30.8 ml of 31% hydrochloric acid are added and the batch is stirred at room temperature for 8 hours. A further 25.1 ml of water and 3.75 ml of 60% acetic acid are added, and the solution is cooled to −5° C.

[0076] b) Solution of Naphtol AS

[0077] A flask is charged with 23.9 g of Naphtol AS in 50.2 ml of water, and 26.7 ml of 25% aqueous sodium hydroxide solution are added. This mixture is then stirred at 60° C. for 120 min to dissolve it. It is rapidly filtered with suction and likewise made up with water to a total volume of 300 ml (˜0.3 M).

[0078] c) Dilute Sodium Nitrite Solution

[0079] A 1 N aqueous sodium nitrite solution is prepared.

[0080] d) Buffer Solution

[0081] A buffer solution is prepared from 4 ml of 60% acetic acid and 600 ml of water.

[0082] e) Diazotization of 2,5-Dichloroaniline in Microreactor

[0083] The 2,5-dichloroaniline hydrochloride solution prepared under a) is adjusted to 100 ml. The reactant solution and the 1 N sodium nitrite solution from c) are pumped via calibrated piston pumps into the respective reactant inlets of the microreactor at a flow rate of 12 ml/min each. The diazotization reaction takes place in the reactor space. The heat exchanger circuit of the microreactor is connected to a thermostat which ensures the desired reaction temperature of about 5° C. The reaction solution emerging from the reactor is bulked with water to 300 ml in a collecting vessel and any excess sodium nitrite present is destroyed with sulfamic acid. The diazonium salt solution (−0.3 M) is used for azo coupling either in a downstream microreactor or in a reaction vessel according to conventional processes.

[0084] f) Azo Coupling to Form C.I. Pigment Red 2 in Microreactor

[0085] The diazonium salt solution prepared by diazotization in a microreactor and also the Naphtol AS solution from b) are pumped via calibrated piston pumps into the respective reactant inlets of the microreactor at a flow rate of 6 ml/min each. The actual azo coupling takes place in the reactor space mentioned. To obtain a buffering effect, these reactant solutions are diluted with an acetic acid buffer prepared according to d), shortly upstream of the reactor inlets. The buffer solution is likewise fed with the aid of calibrated piston pumps into the reactant feed lines of the microreactor at a flow rate of 6 ml/min via a T-junction. The heat exchanger circuit of the microreactor is connected to a thermostat which ensures the desired reaction temperature of about 40° C. The product suspension pH at the reactor outlet is about 3. The product suspension emerging from the reactor is collected in a piston, filtered off with suction and washed neutral with water. The moist pigment is dried at 65° C.

EXAMPLE 3 C.I. Pigment Yellow 191

[0086] a) Preparation of a Suspension of 2B-Acid Hydrochloride

[0087] A 500 ml three-neck flask is charged with 46.2 g of solid 2B-acid (95.6%) (5-amino-3-chloro-2-methylbenzenesulfonic acid) in 400 ml of water, and 18.1 ml of 33% aqueous sodium hydroxide solution are added. The mixture is then heated to 90° C. After addition of 1.6 g of Celite and further stirring at 90° C., the batch is filtered hot. 92.8 ml of 20% hydrochloric acid are added to the filtrate to precipitate the amine hydrochloride.

[0088] b) Conventional Diazotization

[0089] The 2B-acid hydrochloride suspension is diazotized with 26.6 ml of 40% sodium nitrite solution at 20° C. Initially the nitrite is metered in rapidly, while the rest is added at such a rate that there is always a small detectable nitrite excess. The ready-produced diazonium salt suspension is adjusted with water to a total volume of 1 500 ml (about 0.13 molar).

[0090] c) Diazotization of 2B-acid in Microreactor

[0091] The 2B-acid hydrochloride suspension prepared according to a) is adjusted to 1 000 ml. The suspension and 40% of sodium nitrite solution are pumped via calibrated piston pumps into the respective reactant inlets of the microreactor at a flow rate of 40 ml/min and 1 ml/min respectively. The diazotization reaction takes place in the reactor space. The heat exchanger circuit of the microreactor is connected to a thermostat which ensures the desired reaction temperature of about 20° C. The reaction solution emerging from the reactor is stirred in a collection vessel for one hour in the presence of a small excess of nitrite. Water is added to a total volume of 1 500 ml, and any excess sodium nitrite present is destroyed with sulfamic acid. The diazonium salt solution (˜0.13 M) is used for azo coupling either in a downstream microreactor or in a reaction vessel according to conventional processes.

[0092] d) Solution of Pyrazole Acid Three (3-(3-methyl-5-oxo-4,5-dihydropyrazol-1-yl)benzenesulfonic acid)

[0093] A flask is charged with 400 ml of water, and 57.7 g of pyrazole acid three are added. 22.2 ml of 33% aqueous sodium hydroxide solution are added to dissolve the acid. For coupling, the batch is adjusted with water to a total volume of 750 ml or 0.26 M and heated to 40° C.

[0094] e) Azo Coupling in Microreactor

[0095] The diazonium suspension prepared under b) or c) and the pyrazole acid three solution d) are pumped via calibrated piston pumps into the respective reactant inlets of the microreactor at a flow rate of 20 ml/min and 10 ml/min respectively. The actual azo coupling takes place in the reactor space mentioned. The reaction is then carried out at a reaction temperature of 40° C. and a pH of 6.3. The pigment suspension is subsequently stirred at 40° C. for 60 min. It is then heated to 80° C. and maintained at 80° C. for 15 min. A solution of 1.7 mol of CaCl₂, 61 mol of water, 0.0075 mol of sodium hydroxide and 0.01 mol of stearic acid is prepared per mole of pigment and added to the pigment suspension. The batch is stirred at 80° C. for 2 hours, then allowed to cool down to 70° C. and washed with water.

[0096] f) Laking to Form Pigment Yellow 191 in Microreactor

[0097] The pigment suspension is made up to 2 500 ml, heated to 80° C. and maintained at 80° C. for 15 min with stirring.

[0098] 33.4 g of 77% calcium chloride are dissolved in 250 ml of water in a 400 ml beaker. The pigment suspension and the calcium chloride solution are pumped via calibrated piston pumps into the respective reactant inlets of the microreactor at a flow rate of 90 ml/min and 9 ml/min respectively. The thermostat of the heat exchanger circuit of the microreactor is set to a reaction temperature of 85° C. The pigment suspension emerging from the reactor is collected in a stock reservoir vessel.

EXAMPLE 4 C.I. Pigment Red 53:1

[0099] a) Preparation of a Suspension of CLT-Acid Hydrochloride (2-amino-5-chloro-4-methylbenzenesulfonic acid)

[0100] A 500 ml three-neck flask is charged with 44.6 g of solid CLT-acid (99%) in 250 ml of water, and 31 ml of 31% hydrochloric acid are added. The mixture is stirred for 30 min.

[0101] b) Conventional Diazotization

[0102] The CLT-acid hydrochloride suspension is diazotized with 26.6 ml of 40% sodium nitrite solution at 20° C. Initially the nitrite is metered in rapidly, the rest is added at such a rate that a small excess of nitrite is always detectable. The ready-prepared diazonium salt suspension is adjusted with water to a total volume of 1 500 ml (0.13 M).

[0103] c) Diazotization of CLT-Acid in Microreactor

[0104] The CLT-acid hydrochloride suspension prepared under a) is adjusted to 1 000 ml. The suspension and a 40% sodium nitrite solution are pumped via calibrated piston pumps into the respective reactant inlets of the microreactor at a flow rate of 40 ml/min and a flow rate of 1 ml/min respectively. The diazotization reaction takes place in the reactor space. The heat exchanger circuit of the microreactor is connected to a thermostat which shows the desired reaction temperature of about 15° C. The reaction solution emerging from the reactor is warmed to 20° C. with a small excess of nitrite. After a delay time of 60 min, it is made up with water to 1 500 ml and any excess sodium nitrite present is destroyed with sulfamic acid. The diazonium salt solution (˜0.13 M) is used for azo coupling either in a downstream microreactor or in a reaction vessel according to conventional processes.

[0105] d) Solution of β-naphthol

[0106] A flask is charged with 400 ml of water, and 28.1 g of β-naphthol are added. 24.2 ml of 33% strength aqueous sodium hydroxide solution are added to dissolve the naphthol. For coupling, the batch is adjusted with water to a total volume of 750 ml or 0.26 M and heated to 40° C.

[0107] e) Azo Coupling in Microreactor

[0108] The diazonium suspension prepared under b) or c) and the β-naphthol solution d) are pumped via calibrated piston pumps into the respective reactant inlets of the microreactor at a flow rate of 20 ml/min and of 10 ml/min respectively. The actual azo coupling takes place in the reactor space mentioned. The reaction is carried out at a reaction temperature of 40 to 50° C. at a pH of 7.5. The pigment suspension is subsequently stirred at 40° C. and pH 7.5 for 30 min.

[0109] The pigment yield can be increased from 96% to 99% by the following variation: the pigment suspension is adjusted to pH 2.0 with 33% hydrochloric acid in a collecting vessel. After a delay time of about 10-15 min in the collecting vessel, the pigment suspension is pumped into a further microreactor. Sufficient 10% aqueous sodium hydroxide solution is pumped in through the second reactant inlet that, after mixing in the reactor, a pH of 7.5 is obtained at the outlet. The subsequent procedure is as described above, ie. stirring at 40° C. and pH 7.5 for 30 min.

[0110] f) Laking to Form Pigment Red 53:1 in Microreactor

[0111] The pigment suspension is made up to 2 500 ml, heated to 80° C. and maintained at 80° C. for 15 min with stirring.

[0112] 29 g of barium chloride×2 H₂O are dissolved in 250 ml of water in a 400 ml beaker. The pigment suspension and the barium chloride solution are pumped via calibrated piston pumps into the respective reactant inlets of the microreactor at a flow rate of 90 ml/min and 9 ml/min respectively. The thermostat of the heat exchanger circuit of the microreactor is set to a reaction temperature of 85-95° C. The pigment suspension emerging from the reactor is collected in a stock reservoir vessel.

EXAMPLE 5 Water-Soluble Reactive Dyes Reactive Orange 107

[0113] a) Diazotization of Para Base Ester (Conventionally)

[0114] 1.) Diazotization of Para Base Ester (2-(4-aminobenzenesulfonyl)ethyl sulfate)

[0115] 25.5 g of 2-(4-aminobenzenesulfonyl)ethyl sulfate are introduced into 200 g of water with stirring in a 500 ml beaker. 36 g of 31% hydrochloric acid are added dropwise and stirred in for 30 min. The suspension is cooled down to 0 to −5° C. About 20 g of 5N sodium nitrite solution are added dropwise at that temperature over 30 min. The batch is subsequently stirred at about 5° C. for 1-2 hours. Excess nitrite is destroyed with sulfamic acid. The batch is made up with water to 300 ml (0.3 M).

[0116] 2.) Solution of 4-acetylamino-2-aminobenzenesulfonic Acid

[0117] 21 g of 4-acetylamino-2-aminobenzenesulfonic acid are added to 250 g of water and adjusted to pH 4.3 with solid sodium bicarbonate. The solution is filtered with suction, made up to a volume of 300 ml with water (˜0.3 M) and heated to 50° C.

[0118] 3.) Buffer Solution

[0119] A buffer solution is prepared from 75 g of acetic acid (100%) and 66 g of sodium acetate (anhydrous) in 800 g of water.

[0120] b) Azo Coupling in Microreactor

[0121] The diazonium component suspension prepared conventionally under a1) and the solution of 4-acetylamino-2-aminobenzenesulfonic acid a2) are pumped via calibrated piston pumps into the respective reactant inlets of the microreactor at a flow rate of 6 ml/min in each case. The actual azo coupling takes place in the reactor space mentioned. To obtain the pH of 4-4.5 required for the azo coupling, these reactant solutions are diluted with an acetic acid/sodium acetate buffer prepared according to a3), shortly upstream of the reactor inlets. The buffer solution is likewise fed into the reactant feed lines of the microreactor using calibrated piston pumps at a flow rate of 6 ml/min via a T-junction. The heat exchanger circuit of the microreactor is connected to a thermostat which shows the desired reaction temperature of 50° C. The product suspension pH is between 3.8-4.5 at the reactor outlet. The dye solution emerging from the reactor is collected in a flask, adjusted to a pH of 5.5-6.0 with sodium bicarbonate and clarified. The reactive azo dye is isolated by evaporating or spray drying. 

What is claimed is:
 1. A process for preparing azo colorants, which comprises conducting one or more of a) diazotization of aromatic or hetaromatic amines, b) azo coupling, c) laking and d) metal complexing in a microreactor.
 2. The process of claim 1 for preparing azo pigments, wherein the diazotization of aromatic or hetaromatic amines, or the azo coupling, or the laking, or the diazotization and the azo coupling, or the diazotization and the azo coupling and the laking, are carried out in a microreactor.
 3. The process of claim 1 for preparing azo dyes, wherein the diazotization of aromatic or hetaromatic amines, or the azo coupling, or the metal complexing, or the diazotization and the azo coupling, or the diazotization and the azo coupling and the metal complexing, are carried out in a microreactor.
 4. The process of claim 1 , wherein a solution or suspension of aromatic or hetaromatic amine or its ammonium salt and also a solution or suspension of a diazotizing agent are continuously introduced into the microreactor, continuously mixed with each other in the microreactor and reacted.
 5. The process of claim 1 , wherein a solution or suspension of a coupleable diazonium salt and also a solution or suspension of an azo coupling component are continuously introduced into the microreactor, continuously mixed with each other in the microreactor and reacted.
 6. The process of claim 1 , wherein a solution or suspension of an azo colorant that contains acid groups and also a solution or suspension of a metal salt are continuously introduced into the microreactor, continuously mixed with each other in the microreactor and reacted.
 7. The process of claim 1 , wherein the diazotization and subsequent azo coupling are conducted using two or more microreactors connected in series or microreactors having two or more reaction zones.
 8. The process of claim 4 , wherein the introduced solutions or suspensions are brought to the reaction temperature in the interior of the microreactor by means of one or more heat exchangers.
 9. The process of claim 5 , wherein the introduced solutions or suspensions are brought to the reaction temperature in the interior of the microreactor by means of one or more heat exchangers.
 10. The process of claim 6 , wherein the introduced solutions or suspensions are brought to the reaction temperature in the interior of the microreactor by means of one or more heat exchangers.
 11. The process of claim 4 , wherein the suspensions are passed through the reactor in a continuous path without corners or with rounded corners.
 12. The process of claim 5 , wherein the suspensions are passed through the reactor in a continuous path without corners or with rounded corners.
 13. The process of claim 6 , wherein the suspensions are passed through the reactor in a continuous path without corners or with rounded corners.
 14. The process of claim 4 , wherein one or more of the solutions or suspensions, before being introduced into the microreactor, are continuously mixed with a buffer solution via a T-junction.
 15. The process of claim 5 , wherein one or more of the solutions or suspensions, before being introduced into the microreactor, are continuously mixed with a buffer solution via a T-junction.
 16. The process of claim 6 , wherein one or more of the solutions or suspensions, before being introduced into the microreactor, are continuously mixed with a buffer solution via a T-junction.
 17. The process of claim 1 , wherein concentrations, pH values, flow rates and temperatures are captured and controlled via sensors and control circuits integrated in the microreactor. 